Communication systems often use transmission signals focused around a carrier frequency of a defined channel. Information is conveyed by representing the information with a modulation based on amplitude, phase, frequency and/or combinations thereof. The information is sent by one or more signals over a band of frequencies around the carrier frequency.
A radio frequency (RF) power amplifier is often used for modulations, such as amplitude modulation. The RF power amplifier is required to operate over wide ranges of frequencies and power levels. Ideally, perfect linearity over the ranges of frequencies and power levels is desired. However, perfect linearity is impractical to realize in real systems. As a result, RF power amplifiers typically introduce unwanted distortions due to their non linearity. These distortions degrade communications and impact performance.
However, the RF power amplifier typically includes non linearity and introduces unwanted distortions into its output signal. These distortions degrade communications, degrade efficiency and negatively impact performance. Additionally, intermodulation of input signal components can occur and cause undesirable interference. The intermodulation products can also extend outside the allowed bandwidth and cause undesirable interference and violate transmitting licensing and regulatory spectral emission requirements.
One technique to reduce the RF power amplifier introduced distortions is to apply a predistortion the to the amplifier input signal. The predistortion attempts to compensate for the amplifier-introduced distortions and improve the linearity of the cascade consisting of pre-distorter and RF power amplifier. The typical algorithms used for predistortion are intended to tune their parameters and minimize the total error between the desired reference signal and an observed signal. However, the amount or degree of linearization actually achieved can vary substantially according to both instantaneous characteristics of the reference signal being pre-distorted and the amplifier's transfer characteristic.